Plug valves typically include a body having an inlet port, an outlet port and a central chamber extending between the inlet and outlet ports. A plug member is rotatably positioned inside the central chamber sandwiched between an upstream seal segment and a downstream seal segment. Each seal segment includes a through bore that is aligned with the respective inlet and outlet ports to form a flow passage through the plug valve body. The plug member also includes a central bore extending therethrough such that during operation, the plug member rotates between an open position, to align the central bore with the flow passage to facilitate fluid flow through the plug valve, and a closed position, to offset the central bore from the flow passage to block fluid flow through the plug valve.
Plug valves are designed so that the plug member shifts or otherwise “drifts” small amounts in the axial direction relative to the flow of fluid. This drift oftentimes enables fluid particulate to migrate between the plug member and the seal segments. For example, when the plug valve is in a closed position, the plug member drifts apart from the upstream seal segment causing a gap to form between an inner surface of the inlet seal segment and an outer surface of the plug member. As a result, fluid and other fine particles such as, for example, frac sand, that flow through the plug valve will migrate between the seal segment and the plug member, which can accumulate, causing an increase in friction or imbed therebetween, which ultimately diminishes seal performance.